Organic sulfur in fossil fuels causes environmental pollution when combusted and sulfur in petroleum can affect the performance of the refining equipment. High levels of sulfur in gasoline can also deactivate catalyst-based engine exhaust emission control systems (Gonzalez, R. G., Hart's Fuel Technology and Management, November/December 1996, 56-61). Therefore, low sulfur level gasoline is required by government regulation and desired by the refinery and auto industry.
Many biocatalysts and processes have been developed to desulfurize fossil fuels, including those described in U.S. Pat. Nos. 5,356,801, 5,358,870, 5,358,813, 5,198,341, 5,132,219, 5,344,778, 5,104,801 and 5,002,888, incorporated herein by reference. Analyses indicate that a limitation in the commercialization of the technology is the ability of the biocatalysts, such as the bacteria and enzymes that are involved in the desulfurization process, to catabolize or metabolize only specific types of organosulfur compounds. These organosulfur compounds, contain aromatic rings, such as, for example, dibenzothiophene (DBT). Often, other organosulfur compounds, such as thiophene, 2, 2'-bithiophene, 2-methylthiophene and 3-methylthiophene, remain in the refined fossil fuel without significant removal by the biocatalyst.
The most common method for petroleum desulfurization is hydrotreating. However, with increasingly stringent regulations this is becoming more difficult and expensive. Conventional hydrotreating can decrease the sulfur level in FCC gasoline from 1000-2000 parts per million (ppm) to 200 ppm for a relatively low cost. However, it is very expensive to produce FCC gasoline below the 200 ppm specification because the light fraction of the FCC gasoline must also be hydrotreated. Due to the high olefin content of the light fraction, the hydrotreating process involves much higher hydrogen consumption and octane loss due to the saturation of olefins (Gonzalez, R. G. (1996), supra).
Over 90% of the sulfur in gasoline resulting from fluid catalytic cracking occurs in thiophene and substituted thiophenes. Thus, to obtain gasoline meeting current requirements for low sulfur content, methods are needed for removing a substantial amount of the thiophene and substituted thiophenes present in gasoline. Therefore, a need exists for efficient and economical methods for removing thiophene and substituted thiophenes from gasoline.